1. Field of the Invention
The present invention relates to semiconductor wafer processing, and more specifically to optimizing semiconductor wafer cleaning and drying in an integrated unit.
2. Description of the Related Art
Typically, semiconductor wafer fabrication entails multiple processing operations. For example, the processing operations can include many repeated steps, such as implantation, photolithography, material deposition, planarization, and related etching. In between the multiple processing operations, cleaning must be performed to ensure the removal of particulates and unwanted material that adhere to the wafer. Exemplary particulates that can adhere to the surface of the wafer can include silicon dust, silica, slurry residue, polymeric residue, metal flakes, atmospheric dust, plastic particles, and silicate particles.
Cleaning the wafer typically includes the use of deionized water (DIW), chemicals, and chemicals with DIW applied to wafer surfaces using mechanical contact, such as brush scrubbing. The application of the chemicals can also occur by completely immersing the wafer in a chemical or spraying the chemical on the wafer. However, while chemical processing removes most particulates and unwanted material, there may be times when not all particulates or material are removed to the desired degree.
Following the chemical cleaning process, the wafer may be subjected to a spin, rinse and dry (SRD) cycle to further remove chemical residues or particulates. The wafer then exits the SRD cycle in a dry state and ready for the next processing step. This cycle then repeats for any number of layers needed to fabricate a desired integrated circuit device being made from the wafer.
FIG. 1 is a diagram illustrating a wafer cleaning system with brushes. The wafer cleaning system shows a wafer 100 rotating with a wafer spin 110 while disposed between a first brush 120 and a second brush 130, both brushes having multiple nodules 160. First brush 120 has a first through the brush (TTB) conduit 140 and is shown having a first brush rotation 125. Correspondingly, second brush 130 has a second TTB conduit 150 having a second brush rotation 135. While the brushes rotate in the directions shown, thus mechanically assisting in the removal of unwanted material, a chemical can be applied via first TTB conduit 140 and second TTB conduit 150 to chemically remove unwanted material.
The wafer cleaning system is typically housed within a containment chamber to prevent unwanted contamination of the semiconductor wafer fabrication environment. However, by design, brush cleaning will spray processing chemicals and water all over the containment chamber. This spraying, although common in brush scrubbing systems, can have the downside of introducing contaminants from prior scrub brush operations onto later processed wafers. Unfortunately, common prior art brush scrubbing will necessarily spray the process chemicals or water throughout the containment chamber during a brush scrubbing step.
In some processing configurations, brush scrubbing may only be done on one side of the wafer, such as the bottom side. In such cases, either no processing or application of another processing technology is used on the other side of the wafer. Although this is may be done, it is a common objective to not contaminate one side of the wafer with processing being done on the other side. That is, if brush scrubbing is being done on the bottom of the wafer, then it is generally undesirable to allow spraying or dripping of brush fluids on the top side. Although undesirable, such cross-contamination of backside to front side may necessarily occur due to the nature of the rotating brush.
Further, although this process can achieve the intended purpose of removing most unwanted material, the wafer cleaning system can leave residual chemicals or water on the wafer even after the SRD cycle. For example, residual chemicals can remain on the wafer, causing imperfections similar to water spots. These imperfections may then remain under subsequent deposition and etching processes. Cumulatively, the imperfections may, in some situations, cause faults in the electrical connections of circuits being formed in the wafer. Of course, this may result in lower yields from the resulting wafer.
Accordingly, what is needed is an apparatus and method to remove imperfections introduced by the wafer cleaning system while continuing to remove unwanted material from the wafer.